1,696 research outputs found
Combining spectroscopic and photometric surveys using angular cross-correlations II: Parameter constraints from different physical effects
Future spectroscopic and photometric surveys will measure accurate positions
and shapes of an increasing number of galaxies. In the previous paper of this
series we studied the effects of Redshift Space Distortions (RSD), baryon
acoustic oscillations (BAO) and Weak gravitational Lensing (WL) using angular
cross-correlation. Here, we provide a new forecast that explores the
contribution of including different observables, physical effects (galaxy bias,
WL, RSD, BAO) and approximations (non-linearities, Limber approximation,
covariance between probes). The radial information is included by using the
cross-correlation of separate narrow redshift bins. For the auto correlation
the separation of galaxy pairs is mostly transverse, while the
cross-correlations also includes a radial component. We study how this
information adds to our figure of merit (FoM), which includes the dark energy
equation of state and the growth history, parameterized by . We
show that the Limber approximation and galaxy bias are the most critical
ingredients to the modelling of correlations. Adding WL increases our FoM by
4.8, RSD by 2.1 and BAO by 1.3. We also explore how overlapping surveys perform
under the different assumption and for different figures of merit. Our
qualitative conclusions depend on the survey choices and scales included, but
we find some clear tendencies that highlight the importance of combining
different probes and can be used to guide and optimise survey strategies
Implications of a wavelength dependent PSF for weak lensing measurements
The convolution of galaxy images by the point-spread function (PSF) is the
dominant source of bias for weak gravitational lensing studies, and an accurate
estimate of the PSF is required to obtain unbiased shape measurements. The PSF
estimate for a galaxy depends on its spectral energy distribution (SED),
because the instrumental PSF is generally a function of the wavelength. In this
paper we explore various approaches to determine the resulting `effective' PSF
using broad-band data. Considering the Euclid mission as a reference, we find
that standard SED template fitting methods result in biases that depend on
source redshift, although this may be remedied if the algorithms can be
optimised for this purpose. Using a machine-learning algorithm we show that, at
least in principle, the required accuracy can be achieved with the current
survey parameters. It is also possible to account for the correlations between
photometric redshift and PSF estimates that arise from the use of the same
photometry. We explore the impact of errors in photometric calibration, errors
in the assumed wavelength dependence of the PSF model and limitations of the
adopted template libraries. Our results indicate that the required accuracy for
Euclid can be achieved using the data that are planned to determine photometric
redshifts
Cosmological constraints from multiple tracers in spectroscopic surveys
We use the Fisher matrix formalism to study the expansion and growth history
of the Universe using galaxy clustering with 2D angular cross-correlation
tomography in spectroscopic or high resolution photometric redshift surveys.
The radial information is contained in the cross correlations between narrow
redshift bins. We show how multiple tracers with redshift space distortions
cancel sample variance and arbitrarily improve the constraints on the dark
energy equation of state and the growth parameter in the
noiseless limit. The improvement for multiple tracers quickly increases with
the bias difference between the tracers, up to a factor in
. We model a magnitude limited survey with realistic
density and bias using a conditional luminosity function, finding a factor
1.3-9.0 improvement in -- depending on global
density -- with a split in a halo mass proxy. Partly overlapping redshift bins
improve the constraints in multiple tracer surveys a factor in
. This findings also apply to photometric surveys,
where the effect of using multiple tracers is magnified. We also show large
improvement on the FoM with increasing density, which could be used as a
trade-off to compensate some possible loss with radial resolution.Comment: 20 pages, 15 figure
Combining spectroscopic and photometric surveys using angular cross-correlations I: Algorithm and modelling
Weak lensing (WL) clustering is studied using 2D (angular) coordinates, while
redshift space distortions (RSD) and baryon acoustic oscillations (BAO) use 3D
coordinates, which requires a model dependent conversion of angles and
redshifts into comoving distances. This is the first paper of a series, which
explore modelling multi-tracer galaxy clustering (of WL, BAO and RSD), using
only angular (2D) cross-correlations in thin redshift bins. This involves
evaluating many thousands cross-correlations, each a multidimensional integral,
which is computationally demanding. We present a new algorithm that performs
these calculations as matrix operations.
Nearby narrow redshift bins are intrinsically correlated, which can be used
to recover the full (radial) 3D information. We show that the Limber
approximation does not work well for this task. In the exact calculation, both
the clustering amplitude and the RSD effect increase when decreasing the
redshift bin width. For narrow bins, the cross-correlations has a larger BAO
peak than the auto-correlation because smaller scales are filtered out by the
radial redshift separation. Moreover, the BAO peak shows a second (ghost) peak,
shifted to smaller angles. We explore how WL, RSD and BAO contribute to the
cross-correlations as a function of the redshift bin width and present a first
exploration of non-linear effects and signal-to-noise ratio on these
quantities. This illustrates that the new approach to clustering analysis
provides new insights and is potentially viable in practice
Filling in CMB map missing data using constrained Gaussian realizations
For analyzing maps of the cosmic microwave background sky, it is necessary to
mask out the region around the galactic equator where the parasitic foreground
emission is strongest as well as the brightest compact sources. Since many of
the analyses of the data, particularly those searching for non-Gaussianity of a
primordial origin, are most straightforwardly carried out on full-sky maps, it
is of great interest to develop efficient algorithms for filling in the missing
information in a plausible way. We explore practical algorithms for filling in
based on constrained Gaussian realizations. Although carrying out such
realizations is in principle straightforward, for finely pixelized maps as will
be required for the Planck analysis a direct brute force method is not
numerically tractable. We present some concrete solutions to this problem, both
on a spatially flat sky with periodic boundary conditions and on the pixelized
sphere. One approach is to solve the linear system with an appropriately
preconditioned conjugate gradient method. While this approach was successfully
implemented on a rectangular domain with periodic boundary conditions and
worked even for very wide masked regions, we found that the method failed on
the pixelized sphere for reasons that we explain here. We present an approach
that works for full-sky pixelized maps on the sphere involving a kernel-based
multi-resolution Laplace solver followed by a series of conjugate gradient
corrections near the boundary of the mask.Comment: 22 pages, 14 figures, minor changes, a few missing references adde
- …